This invention relates to explosives detection at, for example, airports and other transportation terminals, and more particularly, to a method and apparatus for detecting explosives and other materials using resonance fluorescence, resonance absorption, and other electromagnetic processes with a continuous spectrum of photons.
Most explosive materials have relatively high nitrogen and oxygen concentrations. Some common materials also have high nitrogen or high oxygen concentrations; however, almost no common materials have both the high nitrogen and high oxygen concentrations of explosives. Thus, the detection of most explosives would be greatly facilitated if the abundances of nitrogen and oxygen in a sample could be determined. Practically a 100% certainty of identification could be achieved for most kinds of explosives, including plastic explosives, TNT, dynamite, ammonium nitrate, and nitroglycerin. Detection of other elements, such as chlorine, could further decrease the uncertainty of identification for an even wider range of explosives.
There are many requirements that bomb detecting apparatus at airports must meet. First, the measurements must be reliable. Also, the searches must be non-invasive and non-destructive. Since the articles to be examined can be sizeable, the use of penetrating radiation is attractive; however, the radiation must not leave the baggage radioactive. Radiation should be easy to shield so as to make the environment safe for people without the need for bulky and expensive walls. The capability to image a target is often important in bomb detection. In addition, measurements should not take more than several seconds per piece of baggage. Finally, as there is a need for thousands of these facilities, with several at most airports, cost is an important consideration.